Internal combustion engines are designed to to operate within certain normal operating conditions. Operation outside of the designed normal operating conditions can be harmful to the engine. Two such conditions are oil pressure and rotating speed. Oil pressure serves to lubricate working parts of an internal combustion engine through the circulation of oil. Should the circulation of oil fall below a certain normal level because of insufficient oil pressure, the lubrication of the moving parts may be adversely affected. Similarly, operation at greater than a normal predetermined engine rotation speed may subject the engine to excessive destructive forces.
Ignition in an internal combustion engine, in addition to the above mentioned conditions, affects the performance of the engine. Efficient performance in an internal combustion engine is affected by the timing of the ignition with respect to the position of the piston in its upward travel within the cylinder in which it is housed. An igniter, such as a spark plug, gives ignition to gases in the cylinder to cause an explosion which drives the piston downward. At lower engine speeds, efficient engine performance is generally achieved by having ignition occur concurrently with the point at which the piston reaches its maximum point of upward travel, or the "top dead center". At higher engine speeds efficiency generally dictates that ignition take place at a point before the piston reaches the top dead center. The adjustment of the advance of ignition according to operating speeds of the engine is a major function of an ignition system.
Because efficiency of operation of an engine is dependent upon the relationship of ignition advance and engine rotational speeds, ignition advance in internal combustion engines is frequently controlled dependent on engine operating speed. Known mechanical ignition systems include means for varying the ignition advance mechanically. However, many modern engines utilize electronic ignition systems to control ignition advance. Generally, the electronic systems are employed to provide reliable and accurate ignition advance which is responsive to engine operating speed.
Typical known electronic ignition systems use a crankshaft flywheel position sensor to control the advance of ignition. Optic, magnetic or other suitable sensors capable of detecting positions on a crankshaft flywheel may be used. The flywheel will have positions marked thereupon for inducing responses from the particular sensor used. These types of systems may link the ignition control to the monitoring of predetermined positions of a crankshaft flywheel. The continuing detection of positions on the crankshaft flywheel allows both positional and rotational speed information to be obtained. In such systems the timing of the ignition will vary as a function of the rotational speed of the crankshaft.
Engines in which ignition systems are used may function over a wide range of operating speeds and other variable conditions. These conditions and operating speeds may change rapidly. The performance of the engine can be directly affected by the timing of the ignition. Thus, ignition systems should react predictably and accurately to the changing engine conditions.
To address these needs various electric and electronic ignition systems have been developed in the art. Electric and electronic systems are used to provide consistent and accurate ignition timing over various operating conditions. Several known systems have used integration functions coupled to the position sensor.
A typical system uses an integration circuit that is responsive to pulses proportional to rotational signals obtained by the sensor. The integration circuit is used to establish a dual time varying voltage signal for comparison with a reference voltage source. When the varying voltage is equal to the reference voltage source, an output pulse is initiated. A hysteresis circuit is used to adjust the magnitude of the reference voltage. Various other known ignition systems use integration based circuits in a similar fashion to effect ignition advance that varies with engine rotational speed.
However, such ignition circuits, while varying the ignition advance in relation to rotational speed, do not account for and limit or retard ignition where the rotational speed falls outside of a normal operating range. Similarly, such ignition systems fail to account for some other conditions which can affect engine performance.